| Popis: |
An electrophysiological study of the action of erabutoxin–a, a purified neurotoxin from the sea snake Laticauda semifasciata, was made on the nerve muscle preparation of amphibians. The toxin blocked end-plate potentials and acetylcholine (ACh) potentials of innervated muscle. The effects of the toxin on miniature end-plate potentials was to decrease their frequency and amplitude, and was irreversible after three hr of washing. It did not affect the resting or action potential of muscle fibers, or the action potential of nerve. Preliminary investigations in our laboratory indicate that erabutoxin–a may have a unique blocking action at the presynaptic terminal, where it appears to decrease the release of transmitter. These studies also indicate that the toxin blocks the action of the transmitter at the end-plate of skeletal muscle, blocking irreversibly the nicotinic cholinergic ACh receptors. Additionally, it may block the release of transmitter from the presynaptic terminal without affecting the presynaptic action potential. Additional studies on the retina have shown that erabutoxin–a has no effect on the extracellularity recorded electroretinogram or ganglion cell responses. This indicates that there are probably no cholinergic nicotinic receptors involved in these circuits in the retina of frogs. |
